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Reference Guide
This manual provides a detailed list and usage information regarding input entries, output entries, and parameters available in OptiStruct.
Input Data
Subcase Information Section
Alphabetical listing of the Subcase Information Entries.
FMETHOD
Subcase Information Entry Used to specify the parameters for aerodynamic flutter analysis, by referencing a FLUTTER Bulk Data Entry.

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Overview
OptiStruct is a proven, modern structural solver with comprehensive, accurate and scalable solutions for linear and nonlinear analyses across statics and dynamics, vibrations, acoustics, fatigue, heat transfer, and multiphysics disciplines.
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User Guide
This manual provides detailed information regarding the features, functionality, and simulation methods available in OptiStruct.
Reference Guide
This manual provides a detailed list and usage information regarding input entries, output entries, and parameters available in OptiStruct.
- Input Data
  - Bulk Data Input File
    The input file in OptiStruct is composed of three distinct sections.
  - I/O Options and Subcase Information Entries Guidelines
    The following guidelines apply to all entries in the I/O Options and Subcase Information sections.
  - Bulk Data Guidelines
    The following guidelines apply to all entries in the Bulk Data Entry section.
  - Solution Sequences - Data Selectors
    The Data Selectors table is available in an Excel spreadsheet.
  - Supported Optimization Type Chart
    Supported types of optimization for various analysis sequences are outlined.
  - I/O Options Defaults Summary
  - I/O Options by Function
    Descriptions for individual I/O Option Entries can be accessed by selecting from the links for each entry, listed below in groups according to their purpose and alphabetically on the I/O Options section page.
  - Subcase Information Entries by Function
    Descriptions for individual Subcase Information Entries can be accessed by selecting from the links for each entry, listed below in groups according to their purpose and alphabetically on the Subcase Information Section page.
  - Bulk Data Entries by Function
    Guidelines for using Bulk Data Entries are listed in Bulk Data Guidelines.
  - I/O Options Section
    Alphabetical listing of the I/O Options Entries.
  - Subcase Information Section
    Alphabetical listing of the Subcase Information Entries.
    - A2GG
      Subcase Information Entry The A2GG command can be used to select a direct input fluid-structure coupling matrix.
    - ADIABATIC
      Subcase Information Entry The ADIABATIC entry is used in an implicit nonlinear subcase, to convert the subcase into adiabatic analysis.
    - AESYMXY
      I/O Options and Subcase Information Entry Aerodynamic XY plane of symmetry flag. The AESYMXY command can be used in the case control section to indicate whether the aerodynamic model has symmetry with respect to the ground.
    - AESYMXZ
      I/O Options and Subcase Information Entry Aerodynamic XZ plane of symmetry flag. The AESYMXZ command can be used in the case control section to support symmetric models about the centerline.
    - ANALYSIS
      Subcase Information Entry The ANALYSIS command can be used in the I/O Options section to request that only a finite element analysis be performed (optimization input is ignored). It may also be used in the I/O Options or Subcase Information sections to identify the solution sequence for all subcases or for individual subcases, respectively.
    - B2GG
      Subcase Information Entry The B2GG command can be used to select a direct input viscous damping matrix.
    - BASELIN
      Subcase Information Entry Corrects the acceleration record, due to displacement shift.
    - CMETHOD
      Subcase Information Entry The CMETHOD command can be used to select the method for complex eigenvalue extraction.
    - CMSMETH
      Subcase Information Entry The CMSMETH command can be used to request that only a component mode synthesis solution be performed and to select a component mode synthesis method definition to be used.
    - CNTITF
      Subcase Information Entry Used to activate parameters for contact (S2S and N2S) interference for this subcase.
    - CNTLCK
      Subcase Information Entry Used for preloading a Nonlinear Static Analysis subcase to activate a contact lock for the corresponding preloaded Linear Analysis subcase.
    - CNTNLSUB
      Subcase Information Entry The CNTNLSUB command can be used to continue a nonlinear solution from a preceding nonlinear subcase, and thus create complex loading sequences.
    - CNTSTB
      Subcase Information Entry Activates parameters for stabilization control of contact (S2S and N2S) and Gap Elements (CGAP/CGAPG) for this subcase. This entry is supported with nonlinear static and nonlinear transient analysis types for both small and large displacement cases.
    - CONVG
      Subcase Information Entry The CONVG command can be used in the Subcase Information section to select a corresponding CONVG Bulk Data Entry.
    - DEFORM
      Subcase Information Entry The DEFORM command can be used to select an element deformation set.
    - DESOBJ
      Subcase Information Entry To select a single response definition as the objective function of an optimization, or to select system response definitions when the objective function is the least squares sum of these definitions. The DESOBJ command also indicates if this response is to be minimized or maximized.
    - DESSUB
      Subcase Information Entry The DESSUB command can be used in the Subcase Information section, within a subcase definition, to select a constraint set that is subcase dependent.
    - DESVAR
      Subcase Information Entry The DESVAR command can be used to select a set of design variables for use in an optimization run.
    - DIVERG
      Subcase Information Entry Used to select divergence parameters for static aeroelastic divergence analysis.
    - DLOAD
      Subcase Information Entry Select a dynamic load to be applied in a transient and frequency response analysis subcase. The DLOAD command can also be used to select a user-defined loading curve to be applied in a nonlinear static analysis subcase.
    - DYREL
      Subcase Information Entry Activates adaptive dynamic relaxation for Explicit Dynamic Analysis.
    - EIGVRETRIEVE
      Subcase Information Entry The EIGVRETRIEVE command can be used in the Subcase Information section of Modal Frequency Response or Modal Transient Response analysis to retrieve eigenvalue and eigenvector results of a previously run Normal Modes, Modal Frequency Response, or Modal Transient Analysis from an external data file (.eigv).
    - EIGVSAVE
      Subcase Information Entry The EIGVSAVE command can be used to output eigenvalue and eigenvector results of a Normal Modes, Modal Frequency Response, or Modal Transient Analysis run to an external data file (.eigv).
    - ESLTIME
      Subcase Information Entry The ESLTIME command can be used to select particular time steps for geometric nonlinear response ESLM optimization or Multibody Dynamics ESLM optimization.
    - EXCLUDE
      Subcase Information Entry The EXCLUDE command can be used to select a set of elements to be excluded from a Linear Buckling Analysis.
    - FATDEF
      Subcase Information Entry The FATDEF command can be used to select a FATDEF Bulk Data Entry that will define the elements, and their associated fatigue properties, to be considered for Fatigue Analysis.
    - FATPARM
      Subcase Information Entry The FATPARM command can be used to select a FATPARM Bulk Data Entry that will define the parameters to be used for a Fatigue Analysis.
    - FATSEQ
      Subcase Information Entry The FATSEQ command can be used to indicate that a subcase is a fatigue analysis subcase and to select a FATSEQ Bulk Data Entry that will define the loading sequence for the Fatigue Analysis.
    - FLLWER
      Subcase Information Entry The FLLWER command can be used to activate updating pressure loads and concentrated forces and moments, or to activate updating the amplitude of the dynamic excitation introduced by a time-dependent dynamic load (TLOAD1/TLOAD2 or linear combination of TLOAD1/TLOAD2 only) in every nonlinear iteration for the nodes of elements for a subcase where the forces are dependent on the deformation of the elements.
    - FMETHOD
      Subcase Information Entry Used to specify the parameters for aerodynamic flutter analysis, by referencing a FLUTTER Bulk Data Entry.
    - FREQUENCY
      Subcase Information Entry The FREQUENCY command can be used to select the set of forcing frequencies to be solved in a frequency response problem.
    - FSI
      Subcase Information Entry Identifies a FSI Bulk Data Entry to run Fluid-Structure Interaction Analysis with AcuSolve for a Linear Transient Heat Transfer Subcase or Nonlinear Direct Transient Analysis Subcase.
    - GLOBSUB
      Subcase Information Entry The GLOBSUB entry can be used to select a subcase that references the global structure for Local-Global Analysis and a set of grid points in the local structure that defines the cut surface for displacement.
    - GROUNDCHECK
      Subcase Information Entry The GROUNDCHECK command can be used to perform a Grounding Check Analysis on the stiffness matrix to expose unintentional constraints by moving the model rigidly.
    - IC
      Subcase Information Entry The IC command may be used to select initial conditions for transient (structural and heat transfer) and explicit analysis.
    - IDGLOBAL
      I/O Options and Subcase Information Entry The IDGLOBAL entry can be used in the I/O Options section to convert all entries of the specified type into corresponding global entries.
    - IMPERF
      Subcase Information Entry Defines the initial geometrical imperfection in nonlinear analysis.
    - INIPS
      Subcase Information Entry The INIPS command can be used in the Subcase Information section to define initial plastic strains of elements for nonlinear static analysis.
    - INISTRS
      I/O Options and Subcase Information Entry Defines initial stresses of elements for nonlinear static analysis.
    - INLTVEL
      Subcase Information Entry Used to select an inlet flow velocity boundary condition.
    - INVEL
      Subcase Information Entry Used to select a multibody initial velocity set to be applied in a multibody problem.
    - JOULE
      Subcase Information Entry Used in a heat transfer (steady-state/transient, linear/nonlinear) subcase.
    - K2GG
      Subcase Information Entry The K2GG command can be used to select a direct input stiffness matrix.
    - K2PP
      Subcase Information Entry The K2PP command can be used to select a direct input stiffness matrix, which is not included in normal modes.
    - K42GG
      Subcase Information Entry The K42GG command can be used to select a direct input structural element damping matrix.
    - LABEL
      Subcase Information Entry The LABEL command can be used to provide a subcase with a label.
    - LOAD
      Subcase Information Entry The LOAD command can be used to select a load set to be applied to a particular subcase.
    - LOADJG
      Subcase Information Entry Used in the Subcase Information section to select a load set to be applied to joints which are defined via the JOINTG Bulk Data Entry.
    - LOCATE
      Subcase Information Entry The LOCATE entry can be used to select subcase-specific location (geometric position) of each part in the model.
    - M2GG
      Subcase Information Entry The M2GG command can be used to select a direct input mass matrix.
    - MASSSET
      Subcase Information Entry The MASSSET command can be used to select a linear mass combination.
    - MBSIM
      Subcase Information Entry The MBSIM command can be used to select a Multibody simulation definition to be applied in a Multibody problem.
    - METHOD
      Subcase Information Entry The METHOD command can be used to select a method for real eigenvalue extraction.
    - MFLUID
      Subcase Information Entry The MFLUID command can be used to select the parameters and damp elements and activate the calculation of virtual fluid mass.
    - MINMAX or MAXMIN
      Subcase Information Entry The MINMAX or MAXMIN commands can be used to select normalized response or system identification definitions as the objective function for a "Minmax" or "Maxmin" optimization.
    - MLOAD
      Subcase Information Entry The MLOAD command can be used to select a Multibody load set to be applied in a Multibody problem.
    - MODCHG
      Subcase Information Entry The MODCHG command can be used to remove and/or reactivate contact interfaces and/or elements for this subcase. It is used only for nonlinear analysis.
    - MODESELECT
      I/O Options and Subcase Information Entry Used to select a subset of computed modes in modal dynamic analysis subcases.
    - MODEWEIGHT
      Subcase Information Entry The MODEWEIGHT command can be used to define a multiplier for computed eigenvalues that are to be used in the calculation of the "weighted reciprocal eigenvalue" and "combined compliance index" optimization responses.
    - MODTRAK
      Subcase Information Entry The MODTRAK command can be used to control mode tracking.
    - MOTION
      Subcase Information Entry The MOTION command can be used to select a Multibody motion set to be applied in a multibody problem.
    - MOTNJG
      Subcase Information Entry Used to select the motion applied to corresponding joints.
    - MPC
      Subcase Information Entry The MPC command can be used to select a multi-point constraint set.
    - MSCALE
      Subcase Information Entry Used to control mass scaling in Explicit Dynamic Analysis.
    - NLADAPT
      Subcase Information Entry The NLADAPT entry can be used to select the parameters used for Large Displacement Nonlinear Static Analysis, Small Displacement Nonlinear Static Analysis, and Nonlinear Transient Analysis.
    - NLCTRL
      Subcase Information Entry Used to activate and select the control parameters for Nonlinear Static Analysis and Nonlinear Direct Transient Analysis.
    - NLENRG
      Subcase Information Entry Activates energy variables printout for nonlinear analysis and linear static analysis (with Neuber correction).
    - NLMON
      Subcase Information Entry This NLMON Subcase Information Entry can be used to activate Nonlinear Monitoring for a subcase by referencing a corresponding NLMON Bulk Data Entry.
    - NLOUT
      I/O Options and Subcase Information Entry Selects the incremental result output parameters used for Nonlinear Implicit (Static and Transient) and Nonlinear Explicit Analysis.
    - NLPARM
      Subcase Information Entry The NLPARM command can be used to activate nonlinear solution methods for this subcase and to select the parameters used for Nonlinear Static Analysis, and Nonlinear Direct Transient Analysis.
    - NLPRINT
      Subcase Information Entry Controls the printing of certain information to the _nl.out file for nonlinear analysis.
    - NONLINEAR
      Subcase Information Entry The NONLINEAR command can be used to select a nonlinear dynamic load set for linear and small displacement nonlinear direct transient analyses.
    - NORM
      Subcase Information Entry The NORM command can be used to define a normalization factor used in the computation of the "combined compliance index" optimization response.
    - NSGE
      Subcase Information Entry The NSGE command can be used to select a non-structural damping set. The selector command must appear before the first SUBCASE statement.
    - NSM
      Subcase Information Entry The NSM command can be used to select a non-structural mass set for mass generation.
    - P2G
      Subcase Information Entry The P2G command is used before the first subcase to select a direct input load matrix.
    - P2GSUB
      Subcase Information Entry The P2GSUB command is used in a specific subcase to select a direct input load matrix.
    - PEAKOUT
      Subcase Information Entry The PEAKOUT command can be used to select the criteria for automatic identification of loading frequencies at which result peaks occur. Output result output may then be requested at these "peak" loading frequencies. This entry is supported for frequency response solution sequences only.
    - POST
      I/O Options and Subcase Information Entry Used to request subcase-specific output to separate files.
    - PRETENSION
      Subcase Information Entry The PRETENSION command can be used to select and activate a pretensioning bolt load.
    - RADSND
      Subcase Information Entry The RADSND command can be used to select RADSND Bulk Data to specify sound generation panels and microphone field locations.
    - RANDOM
      Subcase Information Entry Selects the RANDPS and RANDT1 Bulk Data Entries to be used in Random Response Analysis.
    - RENERGY
      Subcase Information Entry Used to output Rotor Energy from Rotor Dynamics using Complex Eigenvalue Analysis for all the subcases or individual subcases, respectively.
    - REPCASE
      Subcase Information Entry The REPCASE command can be used to indicate the start of a repeated subcase definition. This is used for multiple output requests of the same type for the same subcase.
    - REPGLB
      Subcase Information Entry The REPGLB command can be used in the Subcase Information section, before the first subcase statement, to select a report set that is not subcase dependent.
    - REPSUB
      Subcase Information Entry The REPSUB command can be used in the Subcase Information section, within a subcase definition, to select a report set that is subcase dependent.
    - RESVEC
      Subcase Information Entry The RESVEC command can be used to control the calculation of residual vectors.
    - RGYRO
      Subcase Information Entry Identifies a RGYRO Bulk Data Entry that contains information required to implement Rotor Dynamics in Modal Complex Eigenvalue Analysis, Modal Frequency Response Analysis, Static Analysis, Linear Direct Transient Response Analysis and/or Small-Displacement Nonlinear Direct Transient Response Analysis.
    - RSPEC
      Subcase Information Entry The RSPEC command can be used to reference combination rules, excitation degrees-of-freedom, and input spectra for use in response spectrum analysis.
    - SDAMPING
      Subcase Information Entry Used to apply modal damping as a function of natural frequency in modal solutions.
    - SEALL
      Subcase Information Entry Identifies the Superelements for Generation and Assembly for One-Step Superelement Analysis.
    - SEDR
      Subcase Information Entry Defines the Superelement Identification Numbers for which Data Recovery is performed for One-Step Superelement Analysis.
    - SEINTPNT
      Subcase Information Entry The SEINTPNT command can be used to select a set of interior DOF of superelements to be converted to exterior DOF.
    - SENSOR
      Subcase Information Entry References a SENSOR or SENSRAD Bulk Data Entry.
    - SOLVTYP
      Subcase Information Entry Used to select the solver for Static and Dynamic Analysis.
    - SPC
      Subcase Information Entry The SPC command can be used to select a single-point constraint set.
    - SPCP
      Subcase Information Entry Used to select a flow pressure boundary condition.
    - STATSUB
      Subcase Information Entry The STATSUB command can be used to select a static solution subcase.
    - STEADY
      Subcase Information Entry The STEADY command can be used in the subcase information section to activate steady state analysis. It identifies a STEADY Bulk Data Entry that contains information required to activate steady state analysis.
    - SUBCASE
      Subcase Information Entry The SUBCASE command can be used to indicate the start of a new subcase definition.
    - SUBCOM
      Subcase Information Entry Delimits and identifies a combination subcase.
    - SUBMODEL
      Subcase Information Entry The SUBMODEL entry can be used to select a submodel as a set of elements. Subcase entries specific to the selected element set can be used to solve the submodel without affecting the rest of the structure.
    - SUBSEQ
      Subcase Information Entry Gives the coefficients for forming a linear combination of the previous static subcases.
    - SUPER
      Subcase Information Entry The SUPER command can be used in the Subcase Information section to assign a subcase to a superelement or a set of superelements.
    - SUPORT1
      Subcase Information Entry The SUPORT1 command can be used to select a fictitious support set to be applied to the model.
    - TEMPERATURE
      Subcase Information Entry Selects the temperature set to be used in either material property calculations or thermal loading.
    - THIST
      Subcase Information Entry Defines time history output for Explicit Dynamic Analysis.
    - TRIM
      Subcase Information Entry Used to select trim variable constraints by referencing a corresponding TRIM Bulk Data Entry.
    - TSTEP
      Subcase Information Entry The TSTEP command can be used to select integration for transient analysis.
    - TSTEPE
      Subcase Information Entry Can be used to select Explicit Time Step Parameters for Nonlinear Explicit Analysis.
    - TSTEPNL
      Subcase Information Entry The TSTEPNL command can be used to select integration and other parameters for nonlinear implicit dynamics analysis.
    - TSTRU
      Subcase Information Entry The TSTRU command can be used to assign a temperature set identification number to the resulting nodal temperatures of a steady-state heat transfer analysis or the last time step of a transient heat transfer analysis.
    - VISCO
      Subcase Information Entry Used to select viscoelastic parameters to conduct a viscoelastic/creep analysis.
    - WEIGHT
      Subcase Information Entry The WEIGHT command can be used to define a weighting factor (multiplier) for the compliances of individual linear static solution subcases, which are used in the calculation of the "weighted compliance" and "combined compliance index" optimization responses.
    - WEIGHTCHECK
      Subcase Information Entry Used to give a report of the mass properties of entire model, including weight, mass moment of inertia and the center of mass.
  - Bulk Data Section
    Alphabetical listing of the Bulk Data Entries.
  - Element Quality Check
    In order to prevent analyses from being carried out on badly discretized models, an element quality check is incorporated into the pre-processing phase.
  - Material Property Check
    In order to prevent analyses from being carried out on models with poor material definitions, a material property check is incorporated into the pre-processing phase. The material property check is controlled by the CHECKMAT parameter (see the PARAM input format).
- Output Data
- Legacy Data
Example Guide
The OptiStruct Example Guide is a collection of solved examples for various solution sequences and optimization types and provides you with examples of the real-world applications and capabilities of OptiStruct.
Verification Problems
This manual presents solved verification models including NAFEMS problems.
Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding OptiStruct.

FMETHOD

Subcase Information Entry Used to specify the parameters for aerodynamic flutter analysis, by referencing a FLUTTER Bulk Data Entry.

Format

FMETHOD = option

Definitions


Argument	Options	Description
`option`	<ID>	ID Identification number of a FLUTTER Bulk Data Entry. No default (Integer > 0)

Comments

This entry is required for a flutter analysis.
The CMETHOD Subcase Information Entry must also be specified when K-method of flutter analysis is used.